In my ( humble ) opinion, extended plug change intervals is nothing more than a marketing scheme, to suggest to the average person, how little maintenance a vehicle requires.
This also apllies to extended oilchange intervals, and we all know about that subject!
YOU try to get some sparkplugs out of an engine, with aluminum cylinder heads, after 5,6, or 7 years, and see how successful you are.
Can you say stripped threads & mega $$$$ to repair?
